As beverages such as coffee, barley water and toasted tea, liquids obtained by roasting plant raw materials to be roasted, such as coffee beans, barley for barley water and tea leaves for toasted tea, and by percolating the roasted materials with hot water or the like are habitually consumed by many people. In a roasting process, a chemical reaction is caused by thermal energy in a plant raw material to be roasted to produce a characteristic flavor or taste, e.g., a flavor, good body, a bitter taste, an acidity or a sweet taste. People have an extremely strong taste for a fragrant flavor produced by roasting in particular.
It is difficult to heat pieces of plant raw material to be roasted so that the pieces of material are uniformly heated to their inner portions, and there is a problem such that a scorched taste is produced in the roasting process or the degree of roasting is reduced to limit the amount of scorching; central portions of the pieces of plant raw material to be roasted are half roasted; and bitterness and various undesirable tastes in the resulting percolated liquid are increased. Even in a case where a strong heating condition is set to reduce the roasting time, only surface portions of the pieces of plant raw material to be roasted are baked and central portions of the pieces of raw material are not sufficiently heated uniformly and the resulting percolated liquid is only bitter and wanting in body.
Methods of reducing a scorched smell and bitterness in an extracted beverage liquid obtained by water extraction from a roasted plant raw material have therefore been proposed. They are, for example, a method of producing a good grain tea beverage having a reduced scorched smell and bitterness resulting from roasting and having a strong sweet taste and a good flavor, including a grain cleaning process for removing scorched portions of roasted grain (Patent Literature 1), a method of removing bitterness by removing fine particles existing in an extract liquid, particularly fine particles having a particle diameter of 5 micrometers or more (Patent Literature 2), and the like. Modifying an extraction apparatus to remove bitterness and various undesirable tastes has also been proposed. For example, an extraction apparatus loaded with activated carbon having an average pore radius distribution about 30 to 100 angstroms and capable of selectively adsorbing and removing a polymeric dark brown ingredient such as chlorogenic acid polymer, which is an astringent ingredient in a coffee extract liquid, by means of the activated carbon has been proposed (Patent Literature 3). Coffee extraction apparatuses capable of improving the clarity of an extract liquid have also been proposed (Patent Literatures 4 and 5).